pico_i2c_lcd.py

   1 import utime
   2 import gc
   3
   4 from lcd_api import LcdApi
   5 from machine import I2C
   6
   7 # PCF8574 pin definitions
   8 MASK_RS = 0x01       # P0
   9 MASK_RW = 0x02       # P1
  10 MASK_E  = 0x04       # P2
  11
  12 SHIFT_BACKLIGHT = 3  # P3
  13 SHIFT_DATA      = 4  # P4-P7
  14
  15 class I2cLcd(LcdApi):
  16
  17     #Implements a HD44780 character LCD connected via PCF8574 on I2C
  18
  19     def __init__(self, i2c, i2c_addr, num_lines, num_columns):
  20         self.i2c = i2c
  21         self.i2c_addr = i2c_addr
  22         self.i2c.writeto(self.i2c_addr, bytes([0]))
  23         utime.sleep_ms(20)   # Allow LCD time to powerup
  24         # Send reset 3 times
  25         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  26         utime.sleep_ms(5)    # Need to delay at least 4.1 msec
  27         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  28         utime.sleep_ms(1)
  29         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  30         utime.sleep_ms(1)
  31         # Put LCD into 4-bit mode
  32         self.hal_write_init_nibble(self.LCD_FUNCTION)
  33         utime.sleep_ms(1)
  34         LcdApi.__init__(self, num_lines, num_columns)
  35         cmd = self.LCD_FUNCTION
  36         if num_lines > 1:
  37             cmd |= self.LCD_FUNCTION_2LINES
  38         self.hal_write_command(cmd)
  39         gc.collect()
  40
  41     def hal_write_init_nibble(self, nibble):
  42         # Writes an initialization nibble to the LCD.
  43         # This particular function is only used during initialization.
  44         byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
  45         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  46         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  47         gc.collect()
  48
  49     def hal_backlight_on(self):
  50         # Allows the hal layer to turn the backlight on
  51         self.i2c.writeto(self.i2c_addr, bytes([1 << SHIFT_BACKLIGHT]))
  52         gc.collect()
  53
  54     def hal_backlight_off(self):
  55         #Allows the hal layer to turn the backlight off
  56         self.i2c.writeto(self.i2c_addr, bytes([0]))
  57         gc.collect()
  58
  59     def hal_write_command(self, cmd):
  60         # Write a command to the LCD. Data is latched on the falling edge of E.
  61         byte = ((self.backlight << SHIFT_BACKLIGHT) |
  62                 (((cmd >> 4) & 0x0f) << SHIFT_DATA))
  63         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  64         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  65         byte = ((self.backlight << SHIFT_BACKLIGHT) |
  66                 ((cmd & 0x0f) << SHIFT_DATA))
  67         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  68         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  69         if cmd <= 3:
  70             # The home and clear commands require a worst case delay of 4.1 msec
  71             utime.sleep_ms(5)
  72         gc.collect()
  73
  74     def hal_write_data(self, data):
  75         # Write data to the LCD. Data is latched on the falling edge of E.
  76         byte = (MASK_RS |
  77                 (self.backlight << SHIFT_BACKLIGHT) |
  78                 (((data >> 4) & 0x0f) << SHIFT_DATA))
  79         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  80         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  81         byte = (MASK_RS |
  82                 (self.backlight << SHIFT_BACKLIGHT) |
  83                 ((data & 0x0f) << SHIFT_DATA))
  84         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  85         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  86         gc.collect()